Production of arylhalosilanes



Patented Sept. 23, 1952 rnonno'r on or ARYLHALOSILANES Arthur J. Barry, Midland, Mich., assignor to Dow 1 v V Corning Corporation, Midland, Mich a corporationof Michigan No Drawing. Application April 10, 1950, Serial In Great Britain December 4,

v 11 Claims. (01. ESE-448.2)

This invention relatesv tothe manufacture of aromatic halosilanes. It. is particularly concerned with an improved process for. the manufacture of: an organohalosilane in which one valence of the silicon atom is satisfied by direct linkage to a carbon atom in abenzenoid hydro v monohydrosilane to produce either aryltrichlorosilane or arylorganodichlorosilane respectively.

The use of the boron'halide catalysts in this reaction resulted in improved yields at lower temperatures. However, both BCls and BF: are expensive compounds. They are diiiicultto handle because of their volatile, toxic natures. They-are extremely unstable toward water, even atmospheric moisture causing their immediate hydrolysis. They may be recovered from the products of reactions in which they have been used as catalysts, but their low boiling points make such recovery an expensive operation. Objects of the-present invention are to provide an improved process for effecting inter action'of benzenoid hydrocarbons and polyhalomonohydrosilanes;forthe provision of improved catalysts-ior' said interacticni and for the production of aromatic halosilanes in high yield with accompanyinglow yields of by-products.

Other objects and advantages will beapparent from the following'description; H It has been found that a benz'e'noid hydrocarbon, free of aliphatic-unsa-turation in any side chains, may be reacted with apolyhalomonohydrosil'anein the-presencejof a silicon-borate complex,"at a reaction temperature above-150 C. and undersufiicient pressure that at least a portion of the reaction mixture is'in a condensed phase, to produce ar'ylhalos ilanes.

Benzenoid hydrocarbons with which this invention is concerned include benzene, polyphen yls such as bipheny-l and napthalene', and alkyl substituted benzenes such, as toluene, xylene, cumene, and me sitylene. Inasmuch as cracking of side chains is obtainedto some extent with such materials as cumene and relatively pure products are obtained when the side chains contain but one. carbon atom each, it is preferred to employ benzene, a polyphenyl, or the methyl derivatives of benzene as the hydrocarbon. 1

The .polyhalomonohydrosilaneswhich are suitable; for usein this process are compounds'havingx-thei general formula: RtH'SiCIa-e, 'in which -Rtrepres'entsa monovalent hydrocarbon radical free of aliphatic. unsaturation andnis an integer of from 0 to; 1. The preferred polyhaloe. monohydrosilanes are HSiCla, CHBHSiQlz, and CsHsHSiClz. 4 V The silicon-borate complex which is employed isone in which at least some, but only a portion, ofthe valences of the silicon and boron are-satis-. fied by substituents of. the'group consistingofphenyl, methyl, alkoxy, chlorine, and hydrogen, and the'remaining valences of the silicon and boron aresatisfied by oxygen atoms, the valences; of which-are; linked to: the silicon and boron atoms of the complex-.- 7 p a j The SillCOli bOlflIB complexes are employedina proportion such that atjleast' 0.01 percent and generally less than 0.5 per cent of boron ispresent, based on the total weight of the' reactants, though larger proportions maybev em: ployed if desired; v I y The complexes employed may be either rela: tively simple identifiable materials or of -such complexity that identification of; molecular. spacies is impossible. The compound [(CHsMSiOlaB exemplifies the identifiable type of complex; The more complex types" may take such iorms'as i in situ in the reaction mixture or maybe presilanesare pared in advance and mixture; 7

' The complexes maybe formed by the'interaction of a silane and a compound of boron. The silanes which are suitable for the formation of the present complex are of the generalforinula R'4abHaSiXb, where each R represents a monovalent hydrocarbon radical, each. X is selected from the group consisting" of alkoxy and chlorine, a is an integer of" from 0 to 1, b is an integer of from 1 to'4; and the sum of a and b is not greater than 4. [Examples of suitable added to the re'action Y SiCl4,;HSiCl3, CHaHSiClz, wmnsuocnnrr 4on3) sSiOCzHs, (one sSiCl, CsHsSiCl'a:-.

csnsongsiqn, cannons) zSiClT and the like. If an alkoxy substituted silane is used, it is preferable that the alkoxy group contain less than 5 carbon atoms. employed for the preparation of the complexes may be in the form of boric acid, boric anhydride, or organic borates such as tributylborate, phenylboric acid: CsH5B(QH)2, and diphenylboric acid: (CGH5)ZBOH. Likewise the complexes hereof may be formed by the interaction of siloxanes or silanols with boron halides or organoboronhalides such as phenylboron dichloride and diphenylboron chloride. When silicon halides are also present, complexes may be formed fro metallic boron or the boron hydrides.

When the complex is previously prepared and added to the reaction mixture, the reaction of the silane and the boron material may be efiected generally at or below reflux temperature at atmospheric pressure. An excess of silane may be employed if desired to act as a solvent for the complex formed, though many of the complexes are liquid products. When B203 is used as the source of boron or when low-boiling silanes such as'-SiCl4 and HSiCla are employed as the source of silicon, higher temperatures than reflux temperature are generally desirable in order to produce'a soluble complex in a short reaction time. Accordingly, in such procedures super atmospheric pressure may be employed in order to obtain higher temperatures for liquid phase reaction.

'When the complex is formed in situ in the reaction mixture, the silane forming the complex is one of the silanes present in the reaction mixture. The boron employed is preferably a com-- pound of the general formula (RJ'cOhBz-c, where R" is a substituent of the group consisting of monovalent hydrocarbon radicals and hydrogen and c is an integer from. 0 to 1. Thus, for example, when benzene and silico-chloroform are being reacted, boric acid may be added to the reaction mixture. The boric acid will interact with the silicochloroform to form a complex which then acts as a catalyst for the interaction of the remaining silicochloroform with the benzene.

Materials such as H3303 and E203 may be used for the in situ formation of the catalyst complexes in either batch-wise or continuous processes. They are more satisfactory, however, in a batch-wise process than in a continuous process, due to the mechanical difiiculties involved in using solid materials in most continuous process types of high pressure apparatus. Thus, in a continuous process, it is preferred to employ either a liquid organoborate or a solution of one of the pre-formed siliconborate complexes as the catalyst.

. The silicon-borate complexes have been found in the products of the BC13 catalyzed reaction of benzene and HSiCh when combined oxygen is present in the system as water or siloxane oxygen. -If such a system is completely anhydrous and free of combined oxygen, all B01: in the system can be recovered as such. However, when there -is'moisture introduced or any siloxane present in the system, the BCh reacts in such 'a manner that silicon-borate complexes are formed. Under these conditions, metallic boron or the boron hydrides and organoboron halides The boron 4 definitely. In such recycling, any loss of catalyst can be made up by addition of the necessary amount of B013 or any of the other boron compounds herein disclosed.

The process of the present invention is operable over a wide range of proportions of polyhalomonohydrosilane and hydrocarbon in the reaction mixture. However, based upon economics and the law of mass action, it is preferable to have less than mols of either of the reactants per mol of the other reactant.

When it is desired to direct the process toward the production of monosilyl derivatives of the benzenoid hydrocarbons, it is preferable to operate with a slight excess of the hydrocarbon. The use of mixtures which contain 'more'tlian one molecular equivalent of the silane per mol of. hydrocarbon results in an increase in the amount of polysilyl derivatives of the hydrocarbon. Thus,- with these larger proportions of the silane, substantially increased amounts of'bis and tris silyl hydrocarbons are obtained without appreciable decrease in the amount of the monosilyl hydrocarbon produced.

In a preferred form of the present invention, the reactants are heated at a reaction temperature above C. At temperatures abov 420 C. no advantage over conducting the reaction without catalyst is obtained. When the polyhalomonohydrosilane is trichlorosilane, the preferred reaction temperature is from 230 C.to 300 C. When the polyhalomonohydrosilane is an organohalomonohydrosilane, such as CHaI-ISiClz, the preferred reaction temperature is from 150 C. to 250 C.

Th pressure employed should be sufiicient to ensure that at the temperature of operation at least a portion of the reaction mixture is in a condensed phase. Thus, when the operation is conducted at a temperature below the critical temperature of the hydrocarbon the pressure should be suflicient to maintain some liquid phase. When the temperature is above the critical temperature of the hydrocarbon, the pressure should be at least the critical pressure thereof whereby a condensed phase is present, though present day knowledge of the nature of this state is incomplete. This may be accomplished in various ways, such as by introducing the reactants continuously into the reaction zone under pressure, or by operating under autogenous pressure in a closed system. The indicated phase condition is obtained when there is employed at least 1.2 gram mole of reactants per liter of reactor volume.

The following examples describe specific em bodiments of the invention, but are not to be construed as limiting th scope thereof. The per cent yield of product in these examples is based on the amount of polyhalomonohydrosilane consumed in the reaction, and is calculated from the following equation: per cent yieldzmols of productXlOO/mols of RnHSiC13-n loaded minus mole of RnHSiCl3-n recovered. Any RinHSiClJ-n which is neither recovered as such nor converted to product, has entered into the by-production of other halosilanes such as RmSiCLi-n and the bisor tris-silyl-hydrocarbons.

Example 1 hours in a 14.4 liter bomb. The maximum pressure attained within the bomb during the heating period was 1025 pounds per square inch. Fractionaldistillaticn or the prcductgave 1298:;grams phenyltrichlorosilane, a 40.8 per cent'yieldu:

Example 2;-

A mixture of 1402. grams. benzene, .2440; grams trichlorosilane, and :39 gramsBzOapwem heated; at an average temperature of 294 (1?; for:16- hcursin a 14. liter bomb. The, maximumipressure, developed within the; bomb during :the heating period was.v 1050 Pounds per square inch; Fractional distillation of. the; reaction product gave; 97.? grams phenyltrichlorosilane; .a. 3.7 .5; per cent yield;

Example 3 Amixture of; 597 grams (5.5111018) (CI-Ir) aSiCl.

and 93 grams. (1.5 mols') HsBO'a washeatedito 57-78" C; and allowed. to reflux; 01740 hours. H01 was 'evolved'throughonti most of; the reflux period. During. the'last' l'lihoursof reflux; a constant. pot temperature 013. 789 C. was. reached and maintained. Fractionation of the reaction product yielded 260.8 grams'ofthedesired'product, [(CH3)'3SiO]3B, boiling at47 'C..at an absolute pressure of 5 mm. mercury. and. havinga refraetive'indexat 25 C; of113852. AZxlliter bomb was loaded with 468 grams benzene, 542 grams HSiCls, and 25 grains of the [(CH3)aSiOl3B prepared above; The reactants-were heated at an average ternperature or 275 C. for 7 hours.

Fractionation of the-reaction product-gave 108 a gramsof CsHsSiCls, a 359 prcent yieldl I Example 4 -A' mixture of 624 grams benzene, 460 grams CHiHSiClz, and-27 gramsoif the ['(CHslaSiOliB from Examp le 3 was heatedin a 2.4 liter bomb for 7 hours at 200 to210 C. Fractionation of the reaction product gave unreacted CI-IsHSiCl-i and benzene, and 194 grams CeI-IsUHsSiClz, a 46 per cent yield. 7 i V Exampiec A mixture of- 142 grams OfCsHs (CH1?) zsiGland 15.5 grams H330 was heated for 16 hours'at 150-160 G. with vigorousevolution of H01. The

liquid reaction product was heldunder slightly reduced pressure to remove any remaining dissolved 'I-ICl. This resultedin a slightlyhazysolution which was analyzed and found to contain 3.45 per cent'by weight of boron; A mixture of 47 grams of. this solution, ifiiigrams benzene, and 5&2 grams of HSiCl washeated in a 2.4 literbcinb for 7 hours at about2'75 'C; V Fractionationof the reaction product yielded 295fgrams C6H5$iC13,

a 45.6 per cent yield.

Example 6 n When 50 grams of the. silicon-borate solution prepared in Example 5, 552 grams tolue'n'e and 460 grainsv CH3HSiClz. are heated a 2.4 liter bomb for 16 hours at a. temperatureof 180 0.,

tolylmethyldichlorosilane is obtained Example 7 5 A mixture of 62 grams H3303 and 345 grams of CHsI-ISiClz was refluxed. for 48 hours, with evolution. oil-101.. The liquid portionof the reaction product was decanted ofl; and analysis showed it. contained 1.8 per cent by weight of boron. A mixture of 55 grams of this solution, 624 grams benzene, and 460=grams of CH3HSiC12 :was heated in a 2.4 literbomb for Tflhours at -200 to- 210 C. Fractionationfof the-J reaction product gave 217 grams of CeHsCHaSiClz, a 35.2 per cent yield.

' Exam Plait A. nuxturecrcerns c i and'HcBOa was refluxed for 16 hours. With evolution or 301. Theiliquid portion ofthe: reaction productconta.ined 0198:

per centboron by'weigh't. .1 A mixture of 96 grams of this liquid, 468'grams benzene, and 5 i2 gram's' HSiCIs was heated-in;a2.4 literbombi'or? hours:

at about 275" C. Fractionation of'the reactiQ product gave 2761grams' of CeHsSiCh, a 16.4 Per centIyield. I 1

' E zz efl When" a. mixture-0112776.. grams of biphenyl;

Z llOgrams, HSiClz, and/1.00. grams oithe;

reaction product from .Example {3 are, heated-in a 142k liter bomb foruiehcursat 300 0., two rise...- meric biphenylyltrichlorosilanes are produced. One is a liquid which disti-lls at from 200-202 C. at 30.. mm. mercuryabsolute pressure,- and. the other is a.v white, crystalline material whichdis- To this 22' grams of HsBOs-were added, causing" evolution of HCL- The mixturewas heated at "25 C; until no solids remained, and then wasput under vacuum to remove dissolved l-ICl. A-clear solution was obtained which had an analysis or 3.05'p'er cent by w'eightof boron, andwhichwas comprised essentially of theco'rnpoun'd I tronaiiozn osioisn v Y I A mixture'ot 33 grams of'thissolution, 624' grams benzene, and 460 gramsCI-IHSiClz was heated'in a 2.4'1iter bomb for 7 hours at2'00? 210 C. I lirac tionation ofthe reaction product gave 206 gram of CoHsCHsSiClz, a'42;2 per-cent yield.

Example 12 v A A mixture of benzeneand trichlorosilane; in a molar ratio of1'.5 to 1.0, and E013 in an amount equal to 0.5 per cent by weight ofthe reactants, was:'-heated in condensed phase at about 275 C. for- 16hours. The benzene used was knownto becontaminated with a small amount of-miscellaneous organosiloxanes. The reaction product was fractionated. to remove unreacted HSiCls.

benzene, and product CsHSiCIa. When the CeHsSiClx had been substantially removedg the distillation residue was found to: contain 0.46 per cent by weightijof boron. This residue is referred to; hereinafter as catalyst A. Fractionation-of 'a portion of catalyst A was continued to isolate materialsboiling. above CcHsSiCls. .Two:;boron- .rich; fractions were obtained; The: first"; (catalyst 13;) boiled in the range ofifromrflfitvflfl?"Ciaitan absolute pressure of 15 mm. mercury. It had a specific gravity at 25 C. of 1.261, and was found to contain 1.03 per cent b weight of boron. The second fraction (catalyst C) boiled in the range of from l06-159 C. at 14 mm. pressure. It had a specific gravity at 25 C. of 1.325, and was found to contain 1.02 per cent by weight of boron.

vThree runs were made in the 2.4 liter bomb in each of which the reactants were 468 grams benzene and 542 grams HSiCls. A reaction period of '7 hours at an average temperature of 275 C. was allowed for each run. In the first run, 202 grams of "catalyst A were used. Fractionation of the reaction product gave 24'! grams of CsHsSiCh,'a 56.1 per cent yield. In the second run, 60 grams of catalyst B wereused. Fractionation gave 382 grams CcHsSiCls, a 55.9 per cent yield. In the third run, 60 grams of catalyst C were'used, and 375 grams of CcHaSiCla were obtained, which was a 54.8 per cent yield.

Example 13 A mixture of 468 grams of benzene, Z08 grams CsHsHSiClz, and '60 grams of catalyst B from Example 12 was heated in a 2.4 liter bomb for 16 hours at 200 C. Fractionation of the reaction product yielded (CsH5)2SiC12.

Example 14 A mixture of 380 grams of naphthalene, 407 grams of trichlorosilane, and 20 grams of the compound [(CH3)3SlO]3B prepared in Example 3 was heated in a 2.4 liter bomb for 16 hours at about 280 C. Fractionation of the reaction product yielded naphthyltrichlorosilane and dihydronaphthyltrichlorosilane.

-That whichis claimed is: a

1. The process which comprises reacting a benzenoid hydrocarbon free of aliphatic unsaturation in any side chains with a polyhalomonohydrosilane of the general formula RnHSlC13-n, in which R represents a monovalent hydrocarbon radical free'of aliphatic unsaturation and n is an integer of from to l, at a reaction temperature of from 150 C. to 420 C., at least a portion of the reaction mixture being in condensed phase; in the presence of a silicon-borate complex selected from the group consisting of (1) the reaction product of a silane of the general formula R'4-abHaSiXb where each R represents a monovalent hydrocarbon radical, each X is selected from the group consisting of alkoxy and chlorine, a is an integer of from 0 to 1, b is an integer of from 1 to 4, and the sum of a and b is not greater than '4; with a compound selected from the group consisting of B203 and compounds of the general formula (RO) :rBR3-a: where R" is selected from the group consisting of monovalent hydrocarbon radicals and hydrogen, R is as defined above, and :r is an integer of from 1 to 3 inclusive; and (2) the reaction product of a silicon compound selected from the group consisting of siloxanes and silanols with a compound of the general formula Rrg/BY3-y where R is a monovalent hydrocarbon radical free of aliphatic unsaturation, Y is a halogen atom and y is an integer of from 0 to 3 inclusive; whereby to produce an arylchlorosilane. I 2. The process of claim 1 in which the polyhalomonohydrosilane is of the general formula (CH3) nHslC13 n in which n is an integer of from 0 to 1.

3. The process of claim 1 in which the ben "zenoid hydrocarbon is benzene, the polyhalomonohydrosilane is CHaHSiCla, and in which the 8 reactionis conducted at a temperature of from C. to 250 C.

4. The process of claim 1 in which the benzenoid hydrocarbon is benzene, the polyhalomonohydro'silane is HSiCla, and in which the reaction is conducted at a temperature of from 230 C. to 420 C.

5. The process which comprises reacting a mixture of (1) a benzenoid hydrocarbon free of aliphatic unsaturation in any side chains, (2) a polyhalomonohydrosilane of the general formula RnHSiCh-n, in whichR represents a monovalent hydrocarbon radical free of aliphatic unsaturation and n is an integer of from 0 to 1, and (3) a boron compound of the general formula (R"cO)3B2-c, where R is a'substituent of the group consisting of .monovalent hydrocarbon radicals and hydrogen and c is an integer of from 0 to 1; at a reaction temperature of from 150 C. to 420 C., at least a portion of the reaction mixture being in condensed phase, whereby to produce an acrylchlorosilane.

6. The process of claim 5 in which the boron compound is present in such an amount that from 0.01 to 0.5 per cent by weight of boron is present, based on the total weight of the reactants.

7. The process which comprises reacting a mixture of benzene, a polyhalomonohydrosilane of the general formula (CH3)nHSiC13-n where n is an integer of from 0 to 1, and a boron compound of the general formula (R"cO)zB2-, where R" is a substituent of the group consisting of monovalent hydrocarbon radicals and hydrogen and c is an integer from 0 to 1; at a reaction temperature of from 150 C. to 420 C., at least a portion of the reaction mixture being in condensed phase, whereby to produce an ary1chlorosilane.

8. The process of claim 7 in which the boron compound is present in an amount such that from 0.01 to 0.5 per cent by weight of boron is present, based on the total weight of the reactants.

9. The process which comprises reacting a mixture of benzene, a polyhalomonohydrosilane of the general formula (CH3)nHSiC13-n in which n is an integer of from 0 to l, and a silicon-borate complex of the general formula [(CHz) 3-n (CzHsO) 11310133 in which n is an integer of from 0 to 1; at a reaction temperature of from 150 C. to 420 0., at least a portion of. the reaction mixture being in condensed phase, whereby to produce an arylchlorosilane.

10. The process in accordance with claim 9 in which the polyhalomonohydrosilane is CHzHSiClz and in which the reaction is conducted at a temperature of from 150 C. to 250 C.

11. The process in accordance with claim 9 in which the polyhalomonohydrosilane is HSiCls and in which the reaction is conducted at a temperature of from 230 C. to 420 C.

- ARTHUR J. BARRY.

REFERENCES CITED The following references are of record in the file of this patent: 

1. THE PROCESS WHICH COMPRISES REACTING A BENZENOID HYDROCARBON FREE OF ALIPHATIC UNSATURATION IN ANY SIDE CHAINS WITH A POLYHALOMONOHYDROSILANE OF THE GENERAL FORMULA RNHSIC13-N, IN WHICH R REPRESENTS A MONOVALENT HYDROCARBON RADICAL FREE OF ALIPHATIC UNSATURATION AND N IS AN INTEGER OF FROM 0 TO 1, AT A REACTION TEMPERATURE OF FROM 150* C. TO 420* C., AT LEAST A PORTION OF THE REACTION MIXTURE BEING IN CONDESED PHASE; IN THE PRESENCE OF A SILICON-BORATE COMPLEX SELECTED FROM THE GROUP CONSISTING OF (1) THE REACTION PRODUCT OF A SILANE OF THE GENERAL FORMULA R''4-A-BHASIXB WHERE EACH R'' REPRESENTS A MONOVALENT HYDROCARBON RADICAL, EACH X IS SELECTED FROM THE GROUP CONSISTING OF ALKOXY AND CHLORINE A IS AN INTEGER OF FROM 0 TO 1, B IS AN INTEGER OF FROM 10 TO 4, AND THE SUM OF A AND B IS NOT GREATER THAN 4; WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OF B2O3 AND COMPOUNDS OF THE GENERAL FORMULA (R''O)XBR3-X WHERE R'' IS SELECTED FROM THE GROUP CONSISTING OF MONOVALENT HYDROCARBON RADICALS AND HYDROGEN, R S AS DEFINED ABOVE, AND X IS AN INTEGER OF FROM 1 TO 3 INCLUSIVE; AND (2) THE REACTION PRODUCT OF A SILICON COMPOUND SELECTED FROM THE GROUP CONSISTING OF SILOXANES AND SILANOLS WITH A COMPOUND OF THE GENERAL FORMULA RYBY3-Y WHERE R IS A MONOVALENT HYDROCARBON RADICAL FREE OF ALIPHATIC UNSATURATION, Y IS A HALOGEN ATOM AND Y IS AN INTEGER OF FROM 0F TO 3 INCLUSIVE; WHEREBY TO PRODUCE AN ARYLCHLOROSILANE. 